In order to keep the number of weighing processes per time interval as high as possible, in conventional weighing devices it is known to send the measurement signal through only a low-pass filter with a relatively high cutoff frequency. This produces the desired low settling time for the filtered measurement signal. If, in addition to the load to be detected, interference acceleration forces also act on the weighing sensor, for example, in the form of relatively high-frequency vibrations, then such interference on the measurement signal can be eliminated at the output of the weighing device by means of the low-pass filter.
There is also the possibility that not only relatively high-frequency, but also low-frequency interference acceleration forces act on the weighing sensor. Corresponding low-frequency interference acceleration forces can rarely be eliminated with a typical low-pass filter, because, in this case, the cutoff frequency of the low-pass filter must be selected so low that the settling time no longer lies in an acceptable range.
Therefore it is typical to include acceleration forces as a significant noise source in the weight measurement through suitable acceleration sensors and to compensate for these forces with suitable methods. The acceleration sensor signal is used here to correct the measurement signal still containing the noise quantity. Until now, in the case of such known weighing devices, acceleration sensors have been constructed structurally identical to the actual weighing sensors and also oriented identically in the immediate surroundings of the weighing sensors. Acceleration sensors are often loaded with the same preload as the weighing sensors, wherein, in the case of the weighing sensors, the preload can consist of, for example, a balance pan or the transport device of a weighing conveyor.
With these measures, for the acceleration sensor with respect to the (mechanical) interference signals, approximately the same dynamic behavior is achieved that the weighing sensor has with respect to the interference signals. In order also to take into account the actual load force acting on the weighing sensor, the amplification of the noise quantity signal is tracked as a function of the load force or the mass placed on the weighing sensor.
If the weighing sensor is no longer structurally identical to the acceleration sensor, then it is known to realize a fixed image filter that simulates the system behavior of the actual weighing sensor with analog signal processing. The system behavior is influenced by the dynamic behavior of the mechanical components of the weighing sensor. In addition to the system behavior caused by the mechanical components, in the case of certain weighing sensors, electromechanical components also influence the system behavior. For example, in the case of a weighing sensor according to the principle of electrodynamic force compensation, the position controller plays a decisive role. At this point it shall be noted that, in the present description, a weighing sensor is understood as any force transducer that can be used for the purpose of weighing an arbitrary product.
One problem in this state of the art is that the dynamic behavior of the weighing sensor depends on the applied mass, that is, on the load force, and therefore, in the case of changing mass or varying load force, the image filter is no longer optimally adjusted. For example, in the case of typical weighing sensors, the natural resonances of the weighing sensor decrease with increasing load force. One possible solution in this case would be to construct the weighing sensor to be large and stiff with correspondingly very high natural resonances. This, however, runs counter to the demand for smaller structural size and high measurement-related sensitivity, where this feature often plays a significant role.